It's a lot more expensive than when i was a kid, lol. My gma always had a yard full in SLa, fed them scraps and scratch corn, they slept in the trees or a ramshackle shed, or wherever. Times have certainly changed! Temp wise, i have the 250 watt red bulbs. It gets seriously cold up here. I turn them on at freezing and below. That's it - but they stay on from December till March, usually. It's Maine. Frigid. THEY don't really need it at freezing, but idw their water to stiffen up, lol. So it's on. I have to brood February and March babies inside my house until mid May.
Everyone has their own range oc, but i know when i get back down south, i won't use one unless Louisiana suddenly becomes brutally cold like here. They just don't get that cold. They make their own heat, too. The coop, without heat light, is a good 20⁰ warmer than outdoors. I have 60ish birds, though. Less is cooler, i presume. So just a lot of facets to consider. I do have insulation for them and like i said, crazy electric bills!